The present invention relates to a machine with a centrifugal drum for centrifuging the liquid from a wet material and with a stripper for removing the residue from the centrifugal drum. A machine of this kind for preparing coffee extract is described in DE-OS No. 26 26 330. It comprises an extremely complicated gear mechanism for driving the centrifugal drum at different speeds, whereby the axle of the centrifugal drum is provided on one side of the principal driving axle of the machine. The centrifugal drum with its vertical axle is in parts continuously closed and in parts continuously open at the bottom which creates unfavourable working conditions. The machine is principally conceived for continuous working. As a result rapid and complete short time ejection of the coffee grounds after each boiling of individual portions is not possible.
It is also known to construct the centrifugal drum by means of two shells which may be axially shifted together and relative to each other. In a first axial position of the centrifugal drum, one may centrifuge the liquid from the wet material, more particularly by boiling of coffee. In a second axial position of the centrifugal drum, the same is opened by the relative axial displacement of both shells of the drum for radially centrifuging of the coffee grounds. A clean, complete removing of the coffee grounds in this case is practically not possible (DE-OS No. 26 16 296).
It is further known to mount in the centrifugal drum an axially slideable bottom which may be shifted axially for axially ejecting the residue, e.g. coffee grounds in a coffee machine (CH-PS No. 600 847). In this case, it is also difficult to achieve always a nice and rapid cleaning and to provide desirable working reliability.